The disclosure relates generally to a directional coupler, and more particularly to a high-directivity directional coupler that can be provided in a remote unit in a wireless distribution system (WDS).
Wireless customers are increasingly demanding digital data services, such as streaming video signals. At the same time, some wireless customers use their wireless communications devices in areas that are poorly serviced by conventional cellular networks, such as inside certain buildings or areas where there is little cellular coverage. One response to the intersection of these two concerns has been the use of distributed antenna systems (DASs). DASs include remote units configured to receive and transmit communications signals to client devices within the antenna range of the remote units. DASs can be particularly useful when deployed inside buildings or other indoor environments where the wireless communications devices may not otherwise be able to effectively receive radio frequency (RF) signals from a source.
In this regard, FIG. 1 illustrates distribution of communications services to remote coverage areas 100(1)-100(N) of a wireless distribution system (WDS) provided in the form of a DAS 102, wherein ‘N’ is the number of remote coverage areas. These communications services can include cellular services, wireless services, such RF identification (RFID) tracking, Wireless Fidelity (Wi-Fi), local area network (LAN), and wireless LAN (WLAN), wireless solutions (Bluetooth, Wi-Fi Global Positioning System (GPS) signal-based, and others) for location-based services, and combinations thereof, as examples. The remote coverage areas 100(1)-100(N) may be remotely located. In this regard, the remote coverage areas 100(1)-100(N) are created by and centered on remote units 104(1)-104(N) connected to a central unit 106 (e.g., a head-end equipment, a head-end controller, or a head-end unit). The central unit 106 may be communicatively coupled to a signal source 108, for example a base transceiver station (BTS) or a baseband unit (BBU). In this regard, the central unit 106 receives downlink communications signals 110D from the signal source 108 to be distributed to the remote units 104(1)-104(N). The remote units 104(1)-104(N) are configured to receive the downlink communications signals 110D from the central unit 106 over a communications medium 112 to be distributed to the respective remote coverage areas 100(1)-100(N) of the remote units 104(1)-104(N). Each of the remote units 104(1)-104(N) may include an RF transmitter/receiver and a respective antenna 114(1)-114(N) operably connected to the RF transmitter/receiver to wirelessly distribute the communications services to client devices 116 within the respective remote coverage areas 100(1)-100(N). The remote units 104(1)-104(N) are also configured to receive uplink communications signals 110U from the client devices 116 in the respective remote coverage areas 100(1)-100(N) to be distributed to the signal source 108. The size of each of the remote coverage areas 100(1)-100(N) is determined by the amount of RF power transmitted by the respective remote units 104(1)-104(N), receiver sensitivity, antenna gain, and RF environment, as well as by RF transmitter/receiver sensitivity of the client devices 116. The client devices 116 usually have a fixed maximum RF receiver sensitivity, so that the above-mentioned properties of the remote units 104(1)-104(N) mainly determine the size of the respective remote coverage areas 100(1)-100(N).
The remote units 104(1)-104(N) may include power amplifiers 118(1)-118(N), respectively, for amplifying the downlink communications signals 110D to specific power levels before transmitting the downlink communications signals 110D to the client devices 116. As such, it may be necessary to calibrate the power amplifiers 118(1)-118(N) during installation and/or a configuration phase of the DAS 102 to ensure that the downlink communications signals 110D are amplified properly. In a non-limiting example, it is possible to calibrate each of the power amplifiers 118(1)-118(N) using a directional coupler that includes an input port, an output port, a coupled port, and an isolated port.
To calibrate a selected power amplifier among the power amplifiers 118(1)-118(N), the input port of the directional coupler may be coupled to the selected power amplifier to receive a respective downlink communications signal outputted by the selected power amplifier. Test equipment, such as a power detector, may be coupled to the coupled port of the directional coupler to receive a coupled signal that is proportional to the respective downlink communications signal received at the input port. Thus, by measuring a power level of the coupled signal, it may be possible to determine a corresponding power level of the downlink communications signal received at the input port. Accordingly, it may be possible to configure the selected power amplifier to output the respective downlink communications signal at a desired power. In this regard, performance merits of the directional coupler, such as insertion loss, coupling ripple, and directivity, can determine the result of power amplifier calibration, and thus the performance of the remote units 104(1)-104(N).
No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinency of any cited documents.